This really affects the Notification component, but I didn't see it in the list, so I chose the closest one.
Currently JIRA has a global notification scheme that only admins can change. However each user may want his/her own notification scheme. Here's a real world example.
A Project Manager may want notifications when assignee make time estimate/worked entries, but some developers may not want this, but then again some developers may. Bugzilla provided this capability so why not Jira. One way to do it is to show the Notification Scheme interface to ALL users.